A prison (also called a jail or gaol) is a building where convicted criminals are held and incarcinated. Some prisoners are serving long terms or life sentence while some are waiting for trial. Those with short terms are probably locked up in a jail rather than prison.

Prisons are run by the government. Other words for prison include "penitentiary", "jail" or "gaol" (pronounced like "jail"), and "correctional facility".There are also different types of prison or jail which are satellite camp, normal prison, special prison for death rows and maximum security prison. Inmates are forced to wear prison uniform or fatigue with different bright colours from orange, blue, green and more depend on every prison. For instance, some prisoners which are prison workers might wear orange fatigue or some prisoner with bad criminal records wear red uniform and vice versa.

A person who has been charged with a crime, but has not yet been convicted for it in a court, may be sent to prison if:

the police have arrested the person and are deciding whether to send them to court,

Male and female inmates are usually kept in separate locations or in separate prisons. Prisons are usually surrounded by walls and gates. There are usually many locked gates inside the prison to control the inmates.

The inmates sleep in small locked rooms called cells. Cells have a bunk bed, a toilet, and a sink. Inmates are allowed to leave their cell every day for exercise. Some inmates work in the prison during the day, either in a factory or doing cooking or cleaning. Law enforcement officers called prison guards watch the inmates. The manager of a prison is called the warden.

Prisons usually also include other buildings and facilities, such as a chapel, a library, an exercise yard, a gymnasium, an infirmary (small hospital), visiting rooms (for visits from family and lawyers), kitchens, and accommodation for prison staff.

People who think that we should have prisons say that removing people who commit crimes from society prevents them from committing more crimes and punishes them for their behavior. They also say that putting people in prison may also prevent others who are likely to commit similar crimes from committing them.

People who think that we should not put people in prisons say that being put in prison makes people more violent and angry. People who commit minor crimes that are sent to prison meet violent criminals. As well, when people are sent to prison, they cannot see their family or children, which can cause problems for their family. Sometimes people are put in prison who have done nothing wrong. An American theory that is critical of prisons is called the prison industrial complex. People who believe in the prison industrial complex think that private prison companies want lots of people to be put in prison in order to make money.

As of 2006, there are currently nine million people in prison in the world. The United States currently has the most people in prison; it has more than 2 million people in prison. In 2002, both Russia and China also had over 1 million people in prison. In 2003, the United Kingdom had 73,000 people in prison; France and Germany had a similar number of people in prison.

County jail is a term used for local administrative security prisons that are in each county of the United States and for those awaiting trial as well those serving short sentences. Some of these institutions can also hold sentenced maximum security immates and some who are awaiting transport to state prisons if they're convicted of crimes.

state prisons is a term used for prisons that are in each state of the United States and for criminals convicted of crimes that land them in these institutions.